## Critical Power Model – energy and waste

The critical power model is one of the most useful tools for optimising race performance, but why does it work? The answer lies in the connection between the depletion of energy reserves and the accumulation of waste products.

A useful overview of the critical power model can be found in a paper by Clarke and Skiba. It applies well to cycling, where power can be measured directly, and to other sports were velocity can play the role of power. Critical power (CP) is the maximum power that an athlete can sustain for a long time without suffering fatigue. This measure of performance is closely related to other threshold values, including lactate threshold, gas exchange threshold, V̇O2max and functional threshold power (FTP). An advantage of CP is that it is a directly related to performance and can be measured outside a laboratory.

The model is based on empirical observations of how long athletes can sustain levels of power, P, in excess of their personal CP. The time to exhaustion tends to be inversely proportional to the extent that P exceeds CP. This can be described by a simple formula, where excess power multiplied by time to exhaustion, t, is a constant, known as W’ (read as “W-prime”) or anaerobic power capacity.

(P-CP)t=W’

Physics tells us that power multiplied by time is work (or energy). So the model suggests that there is a fixed reserve of energy that is available for use when we exceed our CP. For a typical athlete, this reserve is in the order of 20 to 30 kilojoules.

## Knowing your personal CP and W’ is incredibly useful

Suppose you have a CP of 250W and a W’ of 21.6kJ. You are hoping to complete a 10 mile TT in 24 minutes. This means you can afford to deplete your W’ by 0.9kJ per minute, which equates to 900J in 60 seconds or a rate of 15W. Therefore your target power should be 15W above CP, i.e. 265W. By holding that power your W’ balance would slowly fall to zero over 24 minutes.
Theoretically, you could burn through your entire W’ by sprinting at 1250W for 21.6 seconds.

## Replenishing W’

While it may be possible to maintain constant power on a flat TT or on a steady climb, most race situations involve continual changes of speed. A second aspect of the critical power model is that W’ is slowly replenished as soon as your power drops below CP. The rate of replenishment varies between individuals, but it has a half-time of the order of 3.5 minutes, on gentle recovery.

This means that in a race situation, W’ can recover after an initial drop. By hiding in the peloton and drafting behind other riders, your W’ can accumulate sufficiently to mount a blistering attack, of precisely known power and duration. The chart above, generated in Golden Cheetah, shows the variation of my W’ balance during a criterium race, where I aimed to hit zero in the final sprint. You can even download an app onto your Garmin headset that measures W’ in real time. It is great for criterium racing, but becomes less accurate in longer races if you fail to take on fuel at the recommended rate.

## Physiology

Although I am completely convinced that the critical power model works very well in race situations, I have always had a problem with the idea that W’ is some kind of magical energy reserve that only becomes available when my power exceeds CP. Is there a special biological label that says this glycogen is reserved only for use of when power exceeds CP?

One possible answer is that energy is produced largely by the aerobic system up to CP, but above that level, the anaerobic system has to kick in to produce additional power, hence the name anaerobic work capacity. That sounds reasonable, but the aerobic system burns a mix of two fuels, fat and glucose, while the anaerobic system burns only glucose. The glucose is derived from carbohydrates, stored in the liver and muscles in the form of glycogen. But it is all the same glucose, whether it is used aerobically or anaerobically. The critical power model seems to imply that there is a special reserve of glucose that is held back for anaerobic use. How can this be?

The really significant difference between the two energy systems is that the byproducts of aerobic metabolism are water and exhaled CO2, whereas anaerobic glycolysis produces lactic acid, which dissociates into H+ ions and lactate. Note that two H+ ions are produced from every glucose molecule. The lactate can be used as a fuel, but the accumulation of H+ ions presents a problem, by reducing the pH in the cells and making the blood more acidic. It is the H+ ions rather than the lactate that causes the burning sensation in the muscles.

The body is well equipped to deal with a drop in pH in the blood, in order to prevent the acidity from causing essential proteins to denature. Homeostasis is maintained by buffering agents, such as zwitterions, that mop up the H+ ions. However, if you keep producing more H+ ions by furiously burning glucose anaerobically, the cell environment become increasing hostile, with decreasing levels of intramuscular phosphocreatine and rising inorganic phosphate. The muscles eventually shut down because they simply can’t absorb the oxygen required to maintain the flux of ATP. There is also a theory that a “central governor” in the brain forces you to stop before too much damage ensues.

## You don’t “run out of energy”; your muscles drown in their own waste products

It is acknowledged that the magnitude of the W′ might also be attributed to the accumulation of fatigue-related metabolites, such as H+ and Pi and extracellular K+.

Jones et al

If you reach the point of exhaustion due to an accumulation of deleterious waste products in the muscles, why do we talk about running out of energy? And what does this have to do with W’?

Firstly note that CP represents the maximum rate of aerobic exertion, at which the body is able to maintain steady state. Oxygen, inhaled by the lungs, is transported to the muscles and the CO2 byproduct is exhaled. Note that the CO2 causes some acidity in the blood, but this is comfortably managed by the buffering agents.

The connection between H+ ions and energy is evident in the following simple chemical formula for anaerobic glycolysis. Each glucose molecule produces two lactate ions and two H+ ions, plus energy.

C6H12O6 → 2 CH3COCO2 + 2 H+ + Energy

This means that the number of H+ ions is directly proportional to energy. A W’ of 21.6kJ equates to a precise number of excess H+ ions being produced aerobically. If you maintain power above CP, the H+ ions accumulate, until the muscles stop working.

If you reduce power below CP, you do not accumulate a magic store of additional energy stores. What really happens is that your buffering systems slowly reduce the accumulated H+ ions and other waste products. This means you are able to accommodate addition H+ ions next time you exceed CP and the number of H+ ions equates to the generation a specific amount of energy that can be conveniently labeled W’.

## Conclusion

W’ or anaerobic work capacity acts as a convenient, physically meaningful and measurable proxy for the total accumulated H+ ions and other waste products that your muscles can accommodate before exhaustion is reached. When racing, as in life, is always a good idea to save energy and reduce waste.

### References

Implementation: W’bal its implementation and optimisation, Mark Liversedge

## Supercompensating with Strava

Supercompensation sounds like a reference to an investment banker’s salary, but in fact it describes the body’s ability to adapt positively to a training stimulus. The idea is to attain a higher level of fitness, following a training session, than you had before. In fact, that is generally the point of training. This concept is closely linked to Strava’s Fitness and Freshness charts.

The development of athletic performance requires a delicate balance between an adequate stimulus that drives adaptation and the provision of sufficient recovery time to allow these adaptations to take place

Endocrinology of Physical Activity in Sport, Third Edition

Much has been written about supercompensation, but, as the quotation above highlights, improving your own personal performance depends on
– applying the optimal amount of training stimulus and
– allowing the correct amount of recovery time.

## How does supercompensation work?

A hard training session puts your body under stress. An athlete who is perspiring profusely and complaining of aching limbs experiences similar symptoms to a patient with a severe fever. The stress induced by both of these situations is picked up in the brain by the hypothalamus, which triggers a range of hormonal responses, putting the body into recovery mode.

Physical exercise challenges the muscular-skeletal, cardiovascular and neurological systems. The hormonal response elicits a range of actions around the body, including muscle repair, replenishment of glycogen stores, increase in mitochondria and reinforcement of neural pathways. These processes do not begin until activity has ceased, so, in fact, you become fitter during the rest and recovering phase, rather than while you are actually exercising.

The recovery processes take time and energy. In addition to fuelling before and during exercise, it is important to refuel after a hard training session, particularly during the first 20 minutes.

## Optimal training stimulus

Training stimulus is a function of duration and intensity. Strava measures this as Training Load, which shows up as Training Impulse on your Fitness & Freshness chart. This is similar to other commonly used measures. You should also have in mind what aspect of fitness you need to develop for your target events (endurance, power, sprint etc.).

I recently rode over 200km from London to Brighton and back, which Strava calculated as a Training Load of 400. Unfortunately this probably did not make me much fitter, because it left me greatly fatigued. During the next two days that I spent recovering, my body probably just about reattained its previous base line level of fitness and failed to achieve supercompensation. It was a great ride, but it was also an example of excessive training stimulus .

On the other hand, going for a gentle ride without any strong effort is unlikely to put the body under enough stress to give rise to the desired hormonal response. Any supercompensation is likely to be minimal. Some people might call this “junk training”, because higher duration or intensity is needed, in order to become fitter.

So what is the optimal training stimulus should you aim for? A simple answer is to check your Strava Fitness & Freshness page and set a target Training Load equal to about 1.3 to 1.5 times your current Fitness (quite a hard session). This all links back to how to ramp up your fitness.

## The right recovery time

As mentioned above, you get fitter while you are recovering. Ideally your next training session should be timed to match the peak of supercompensation. The colour coding of the chart provides a traffic light system. If you train again too early, your body will not have time to recover. But if you leave it too long, you miss the opportunity. As a general rule, it is sensible to follow a hard training day with an easier day. It is also very important to take one full rest day per week, where activity is limited to nothing more than a short walk or some stretching. When is comes to recovery, remember that sleep is “Chief nourisher in life’s feast”.

### Functional overreaching (FOR)

Good periodisation of training stimulus and recovery results in beneficial performance adaptation, known as functional overreaching. This stimulates anabolic (muscle building) hormones, such as IGF1 and testosterone, while stress hormones, like cortisol remain low. The athlete sees a steady improvement in performance.

### Nonfunctional overreaching (NFOR)

Nonfunctional overreaching occurs when an athlete is too eager to train again. Without sufficient recovery, the body is only just back to base line when it is hit with another bout of exercise. No time is allowed for the anabolic response. This is throwing away the potential benefits of supercompensation and leads to a stagnation of performance.

### Overtraining syndrome (OTS)

Overtraining syndrome occurs when the next training session begins before the body has fully recovered from the last one. This can be a problem for athletes juggling a high number of training hours with a full-time job. When the endocrine system is put under this level of stress, cortisol, prolactin and creatine kinase tend to rise, while sex steroids become depressed. This results in an accumulation of fatigue and a progressive deterioration of performance.

### When were you last in a fully recovered state?

You can tell which of these situations applies to you, by asking how long has it been since you were in a fully recovered state? If it is days, you should be able to get fitter. If it is weeks, you may be in a state of nonfunctional overreaching. If you have not been in a fully recovered state for months, you have overtraining syndrome. The period taken to recover to a healthy state often has the same timescale.

### How do I know if I am in a fully recovered state?

Various apps use heart rate variability (HRV) as an indicator of recovery. Alternatively, you can activate the sliders for Fatigue and Form on your Strava Fitness & Freshness page and look for positive Form. This is when Fitness is greater than Fatigue. My chart below shows a sustained period of high Fatigue and negative Form in April, suggesting that some of the training in that heavy block may have been somewhat counterproductive, but at least I took a rest week in early May.

## Super compensation

Supercompensation is the underlying mechanism of periodised training. It works on a number of timescales from the days in a weekly plan, to the weeks in a monthly plan and up to the months in the season’s plan. I hope that this read has provided you with super compensation.

## Science for dance performance

This web site is about using science to improve performance. Although my focus has generally been on sport, science can also help artistic performance. Professional dancers face many of the same challenges as elite athletes, but a cultural divide separates the two communities. A recent paper helps to bridge this gap, by showing that scientific advances in managing relative energy deficiency in sport (RED-S) may be of great benefit in the dance world.

## Dance and sport

Professional dancers spend many hours a day training in order to deliver top level performances in high pressure situations. On stage, they are quite literally under the spotlight. They also start young, developing bodies that are able to meet the high level of technical demands required to reach the top. In spite of the similarities with the lives of those in elite sport, artistic performance is viewed differently from athletic performance. A prima ballerina would not consider herself an athlete any more than a sprinter would consider herself a dancer. Strictly Ballroom is dance, whereas figure skating is sport. This separations stretches from the individual participants up to the level of governing bodies.

Athletes in many sports adapt their body composition to gain an advantage, often seeking to achieve “race weight” ahead of competition. In many ways, the situation is more extreme for dancers, particularly those pursuing classic forms such as ballet, who aim for a body shape that meets aesthetic ideals, while maintaining the strength and flexibility to perform.

## Relative energy deficiency in dance

In the paper, dancers were invited to complete an online survey that had been based on previous studies of athletes who were potentially at risk of low energy availability, specifically RED-S. Responses included anthropomorphic data, training and performance hours, injuries and illness, indicators of hormone status and attitudes to eating and weight control.

A RED-S risk score was derived from each dancer’s responses. Of the 247 participants, 57% of females and 29% of males had negative scores, consistent with low energy availability.

Psychological factors proved to be important. Many dancers felt anxious about missing class or rehearsals, in a similar way to athletes who suffer from exercise addiction. These dancers also tended to be more obsessive about controlling their weight and what they eat. Most considered the chances of gaining a leading role to be higher if they lost weight. These kinds of attitudes were observed in an earlier study of male cyclists.

Among the female dancers, some interesting correlations showed up between these mental attitudes and both physical and physiological factors. The more obsessive individuals tended to have a lower body mass index (BMI) particularly when calculated using their lowest weight for their current height. They also tended to have experienced various forms of menstrual disfunction, indicating a disruption to normal hormonal function that has been observed in female athletes in low energy availability.

The large majority of dancers had not heard of Relative Energy Deficiency in Sport, probably because they do not self-identify as sportsmen/sportswomen. Yet the peer pressure of dance schools and dance companies, combined with ever present social media, can lead some dancers to restrict energy intake to levels that are insufficient to meet the high demands of training and performance.

## Fit to dance

The authors hope that the publication of this study will help raise awareness in the dance community of the importance of fuelling for the work required. The fact that physical outcomes are connected, via hormones, to mental attitudes is particularly relevant during the COVD crisis, which has impacted the dance world in such a tragic way. The hope is that dancers will be fully fit and healthy to return to the stage, when the theatres eventually open.

### References

Indicators and correlates of low energy availability in male and female dancers
Nicola Keay, AusDancers Overseas, Gavin Francis

Energy Availability: Concept, Control and Consequences in relative energy deficiency in sport (RED-S)

Low energy availability assessed by a sport-specific questionnaire and clinical interview indicative of bone health, endocrine profile and cycling performance in competitive male cyclists, Nicola Keay, Gavin Francis, Karen Hind

## No drafting

In a fascinating white paper, Bert Blocken, Professor of Civil Engineering at Eindhoven University of Technology, comments on social distancing when applied to walking, running or cycling. His point is that the government recommendations to maintain a distance of 1.5 or 2 metres assume people are standing still indoors or outdoors in calm weather. However, when a person is moving, the majority of particulate droplets are swept along in a trailing slipstream.

Cyclists typically prefer to ride closely behind each other, in order to benefit from the aerodynamic drafting effect. Cycling is currently a permitted form of exercise in the UK, though only if riding alone or with members of your household. Nevertheless, there may be times when you find yourself catching up with a cyclist ahead. In this situation, you should avoid the habitual tendency to move up into the slipstream of the rider in front.

Professor Blocken’s team has performed computational fluid dynamics (CFD) simulations showing the likely spread of micro-droplets behind people moving at different speeds. As the cloud of particles, produced when someone coughs or sneezes, is swept into the slipstream, the heavier droplets, shown in red in the diagram above, fall faster. These are generally thought to be more considerably more contagious. You can see that they can land on the hands and body of the following athlete.

Based on the results, Blocken advises to keep a distance of at least four to five meters behind the leading person while walking in the slipstream, ten meters when running or cycling slowly and at least twenty metres when cycling fast.

Social Distancing v2.0

The recommendation, for overtaking other cyclists, is to start moving into a staggered position some twenty metres behind the rider in front, consistently avoiding the slipstream as you pass.

The results will be reported in a forthcoming peer-reviewed publication. But given the importance of the topic, I recommend that you take a look at the highly accessible three page white paper available here.

## Modelling Strava Fitness and Freshness

Since my blog about Strava Fitness and Freshness has been very popular, I thought it would be interesting to demonstrate a simple model that can help you use these metrics to improve your cycling performance.

As a quick reminder, Strava’s Fitness measure is an exponentially weighted average of your daily Training Load, over the last six weeks or so. Assuming you are using a power meter, it is important to use a correctly calibrated estimate of your Functional Threshold Power (FTP) to obtain an accurate value for the Training Load of each ride. This ensures that a maximal-effort one hour ride gives a value of 100. The exponential weighting means that the benefit of a training ride decays over time, so a hard ride last week has less impact on today’s Fitness than a hard ride yesterday. In fact, if you do nothing, Fitness decays at a rate of about 2.5% per day.

Although Fitness is a time-weighted average, a simple rule of thumb is that your Fitness Score equates to your average daily Training Load over the last month or so. For example, a Fitness level of 50 is consistent with an average daily Training Load (including rest days) of 50. It may be easier to think of this in terms of a total Training Load of 350 per week, which might include a longer ride of 150, a medium ride of 100 and a couple of shorter rides with a Training Load of 50.

## How to get fitter

The way to get fitter is to increase your Training Load. This can be achieved by riding at a higher intensity, increasing the duration of rides or including extra rides. But this needs to be done in a structured way in order be effective. Periodisation is an approach that has been tried and tested over the years. A four-week cycle would typically include three weekly blocks of higher training load, followed by an easier week of recovery. Strava’s Fitness score provides a measure of your progress.

### Modelling Fitness and Fatigue

An exponentially weighted moving average is very easy to model, because it evolves like a Markov Process, having the following property, relating to yesterday’s value and today’s Training Load.
$F_{t} = \lambda * F_{t-1}+\left ( 1-\lambda \right )*TrainingLoad_{t}$
where
$F_{t}$ is Fitness or Fatigue on day t and
$\lambda = exp(-1/42) \approx 0.976$ for Fitness or
$\lambda = exp(-1/7) \approx 0.867$ for Fatigue

This is why your Fitness falls by about 2.4% and your Fatigue eases by about 13.3% after a rest day. The formula makes it straightforward to predict the impact of a training plan stretching out into the future. It is also possible to determine what Training Load is required to achieve a target level of Fitness improvement of a specific time period.

The change in Fitness over the next seven days is called a weekly “ramp”. Aiming for a weekly ramp of 5 would be very ambitious. It turns out that you would need to increase your daily Training Load by 33. That is a substantial extra Training Load of 231 over the next week, particularly because Training Load automatically takes account of a rider’s FTP.

Interestingly, this increase in Training Load is the same, regardless of your starting Fitness. However, stepping up an average Training Load from 30 to 63 per day would require a doubling of work done over the next week, whereas for someone starting at 60, moving up to 93 per day would require a 54% increase in effort for the week.

In both cases, a cyclist would typically require two additional hard training rides, resulting in an accumulation of fatigue, which is picked up by Strava’s Fatigue score. This is a much shorter term moving average of your recent Training Load, over the last week or so. If we assume that you start with a Fatigue score equal to your Fitness score, an increase of 33 in daily Training Load would cause your Fatigue to rise by 21 over the week. If you managed to sustain this over the week, your Form (Fitness minus Fatigue) would fall from zero to -16. Here’s a summary of all the numbers mentioned so far.

Whilst it might be possible to do this for a week, the regime would be very hard to sustain over a three-week block, particularly because you would be going into the second week with significant accumulated fatigue. Training sessions and race performance tend to be compromised when Form drops below -20. Furthermore, if you have increased your Fitness by 5 over a week, you will need to increase Training Load by another 231 for the following week to continue the same upward trajectory, then increase again for the third week. So we conclude that a weekly ramp of 5 is not sustainable over three weeks. Something of the order of 2 or 3 may be more reasonable.

### A steady increase in Fitness

Consider a rider with a Fitness level of 30, who would have a weekly Training Load of around 210 (7 times 30). This might be five weekly commutes and a longer ride on the weekend. A periodised monthly plan could include a ramp of 2, steadily increasing Training Load for three weeks followed by a recovery week of -1, as follows.

This gives a net increase in Fitness of 5 over the month. Fatigue has also risen by 5, but since the rider is fitter, Form ends the month at zero, ready to start the next block of training.

To simplify the calculations, I assumed the same Training Load every day in each week. This is unrealistic in practice, because all athletes need a rest day and training needs to mix up the duration and intensity of individual rides. The fine tuning of weekly rides is a subject for another blog.

### A tougher training block

A rider engaging in a higher level of training, with a Fitness score of 60, may be able to manage weekly ramps of 3, before the recovery week. The following Training Plan would raise Fitness to 67, with sufficient recovery to bring Form back to positive at the end of the month.

### A general plan

The interesting thing about this analysis is that the outcomes of the plans are independent of a rider’s starting Fitness. This is a consequence of the Markov property. So if we describe the ambitious plan as [3,3,3,-2], a rider will see a Fitness improvement of 7, from whatever initial value prevailed: starting at 30, Fitness would go to 37, while the rider starting at 60 would rise to 67.

Similarly, if Form begins at zero, i.e. the starting values of Fitness and Fatigue are equal, then the [3,3,3,-2] plan will always result in a in a net change of 6 in Fatigue over the four weeks.

In the same way, (assuming initial Form of zero) the moderate plan of [2,2,2,-1] would give any rider a net increase of Fitness and Fatigue of 5.

## Cycling Physique

It is easy to assume that successful professional cyclists are all skinny little guys, but if you look at the data, it turns out that they have an average height of 1.80m and an average weight of around 68kg. If we are to believe the figures posted on ProCyclingStats, hardly any professional cyclists would be considered underweight. In fact, they would struggle to perform at the required level if they did not maintain a healthy weight.

### Taller than you might think

According to a study published in 2013 and updated in 2019, the global average height of adult males born in 1996 was 1.71m, but there is considerable regional variation. The vast majority of professional cyclists come from Europe, North America, Russia and the Antipodes where men tend to be taller than those from Asia, Africa and South America. For the 41 Colombians averaging 1.73m, there are 85 Dutch riders with a mean height of 1.84m. See chart below.

Furthermore, road cycling involves a range of disciplines, including sprinting and time trialling, where size and raw power provide an advantage. The peloton includes larger sprinters alongside smaller climbers.

### Not as light as expected

While 68kg for a 1.80m male is certainly slim, it equates to a body mass index of 21 (BMI = weight / (height)²), which is towards the middle of the recommended healthy range. BMI is not a sophisticated measure, as it does not distinguish between fat and muscle. Since muscle is more dense than fat and cyclists tend to have it a higher percentage of lean body mass, they will look slimmer than a lay person of equivalent height and weight. Nevertheless doctors use BMI as a guide and become concerned when it falls below 18.5.

The chart includes over 1,100 professional cyclists, but very few pros would be considered underweight. The majority of riders have a BMI of between 20 and 22. Although Colombian riders (red) tend to be smaller, specialising in climbing, their average BMI of 20.8 is not that different from larger Dutch riders (orange) with a mean BMI of 21.2. The taller Colombians include the sprinters Hodeg, Gaviria and Molano.

### Types of rider

This chart shows the names of a sample of top riders. All-out sprinters tend to have a BMI of around 24, even if they are small like Caleb Ewan. Sprints at the end of more rolling courses are likely to be won by riders with a BMI of 22, such as Greipel, van Avermaet, Sagan, Gaviria, Groenewegen, Bennet and Kwiatkowski. Time trial specialists like Dennis and Thomas have similar physiques, though Dumoulin and Froome are significantly lighter and remarkably similar to each other.

GC contenders Roglic, Kruiswijk and Gorka Izagirre are near the centre of the distribution with a BMI around 21, close to Viviani, who is unusually light for a sprinter. Pinot, Valverde, Dan Martin, the Yates brothers and Pozzovivo appear to be light for their heights. Interestingly climbers such as Quintana, Uran, Alaphilippe, Carapaz and Richie Porte all have a BMI of around 21, whereas Lopez is a bit heavier.

If the figures reported on ProCyclingStats are accurate, George Bennet and Emanuel Buchmann are significantly underweight. Weighting 58kg for a height of 1.80m does not seem to be conducive to strong performance, unless they are extraordinary physical specimens.

### Conclusions

Professional cyclists are lean, but they would not be able to achieve the performance required if they were underweight. It is possible that the weights of individual riders might vary over time by a couple of kilos, moving them a small amount vertically on the chart, but scientific approaches are increasingly employed by expert nutritionists to avoid significant weight loss over longer stage races. The Jumbo Foodcoach app was developed alongside the Jumbo-Visma team and, working with Team Sky, James Morton strove to ensure that athletes fuel for the work required. Excessive weight loss can lead to a range of problems for health and performance.

## Relative Energy Deficit in Sport (RED-S)

Unfortunately an increasing proportion of the population of western society has fallen into the habit consuming far more calories than required, resulting an a huge increase in obesity, with all the associated negative health consequences. At the opposite end of the spectrum, a smaller but important group experiences problems stemming from insufficient energy intake. This group includes certain competitive athletes, especially those involved in sports or dance, where a low body weight confers a performance advantage. A new infographic draws attention to this problem and highlights the fact that the individuals have control over the factors that can put them on the path to optimal health and performance.

## RED-S

The human body requires a certain amount of energy to perform normal metabolic functions, including, maintaining homeostasis, cardiac and brain activity. The daily requirement is around 2,000 kcal for women and 2,500 kcal for men. Additional energy intake is required to balance the energy requirements any physical activities performed.

Athletes and dancers need to eat more than sedentary people, but they can fall into an energy deficit in two ways.

• Reducing energy intake, while maintaining the same training load. This is typically an intentional decision, in order to lose weight, in the belief that this might improve performance. It can also arise unintentionally, perhaps due to failing to calculate energy demands of the training programme.
• Increasing training load, while maintaining the same energy intake. This can often occur unintentionally, as a result of a more intensive training session or a shift into a higher training phase. Some athletes or dancers perform extra training sessions while deliberately failing to eat more, in the hope, once again, that this might improve performance.

While most of the population would benefit from a period of moderate energy deficit. High level athletes and dancers tend to be very lean, to the extent that losing further weight compromises health and performance. The reason is that the endocrine system is forced to react to an energy deficit by scaling back or shutting down key metabolic systems. For example, levels of the sex hormones testosterone and oestrogen can fall, leading to, among other things, reductions in bone density. Unlike men, women have a warning sign, in the form of an interruption or cessation of menstruation. Both men and women with RED-S are likely to suffer from a failure to achieve their peak athletic performance.

## Achieving peak performance

Fortunately athletes have control over the levers that lead to peak performance. These are nutrition, training load and, of course, recovery. Consistently fuelling for the energy required, whilst ensuring that the body has adequate time to recover, allows the endocrine system to trigger the genes that lead to the beneficial outcomes of exercise, such as improved cardiovascular efficiency, effective muscular development, optimal body composition, healthy bones and a fully functional immune system. These are the changes required to reach the highest levels of performance.

## Don’t ride your bike like an astronaut

Astronauts return from the International Space Station with weak bones, due to the lack of gravitational forces. It is surprising to learn that competitive cyclists can experience similar losses in bone density over the period of a race season.

The problem is called Relative Energy Deficiency is Sport (RED-S). This occurs when lean athletes reach a tipping point where the benefits of losing weight become overwhelmed by negative impacts on health. When deprived of sufficient energy intake to match training load, certain metabolic systems become impaired or shut down.

Colleagues from Durham University and I recently published a study investigating what cyclists at risk of RED-S can do to improve their health and performance. It is freely available and written in an accessible way, without the requirement for specialist expertise.

## Race performance

Race performance was measured by the number of British Cycling points accumulated over the season. This was correlated with power (FTP and FTP/kg) and training load. However, changes in energy availability proved to be an important factor. After adjusting for FTP, cyclists who improved their fuelling (green triangles) gained, on average, 95 points more than those who made no change. In contrast, those who restricted their nutrition (red crosses) accumulated 95 fewer points and reported fatigue, illness and injury.

The nutritional advice included recommendations on adequate fuelling before, during and after rides. Also see my previous article on fuelling for the work required.

## Bone health

Competitive road cyclists can fall into an energy deficit due to the long hours of training they complete. Although an initial loss of excess body weight can lead to performance improvements, athletes need to maintain a healthy body mass. The lumbar spine is particularly sensitive to deficiencies of energy availability.

In cyclists, the lower back also fails to benefit from the gravitational stresses of weight-bearing sports. This is why, in addition to nutritional advice, study participants were recommended some basic skeletal loading exercises (yes, that is me in the pictures).

The cyclists fell into three general groups: those who made positive changes to nutrition and skeletal loading, those who made negative changes and the remainder. The resulting changes in bone mineral density over a six month period were striking, with highly statistically significant differences observed between the groups.

Those making positive changes (green triangles) saw significant gains in bone mineral density, while those making negative changes (red crosses) saw equally significant negative losses in bone density. Any individual observation outside the band of the least significant change (LSC) is indicative of a material change in bone health.

## Conclusions

The study provided strong evidence of the benefits of positive changes and the costs of negative changes in nutrition and skeletal loading exercises. It was noted that certain cyclists found it hard to overcome psychological barriers preventing them from deviating from their current routines. It is hoped that such strong statistical results will help these vulnerable athletes make beneficial behavioural changes

## References

Clinical evaluation of education relating to nutrition and skeletal loading in competitive male road cyclists at risk of relative energy deficiency in sports (RED-S): 6-month randomised controlled trial, Nicola Keay, Gavin Francis, Ian Entwistle, Karen Hind. BMJ Open Sport and Exercise Medicine Journal, Volume 5, Issue 1. http://dx.doi.org/10.1136/bmjsem-2019-000523

## Fuel for the work required: periodisation of carbohydrate intake

Last week I attended an event announcing the forthcoming launch of a new fitness app called Pillar. It offers combined training and nutrition advice to help athletes achieve their goals. Pillar is backed by a strong scientific team including Professor James Morton, Team Sky Head of Performance Nutrition, and Professor Graeme Close, England Rugby Head of Performance Nutrition.

James Morton gave a fascinating presentation about the periodisation of carbohydrate (CHO) fuelling, including a detailed description of the nutrition strategy he created to support Chris Froome’s famous 80km attack on stage 19 of the 2018 Giro d’Italia. His recent paper explains the underlying science. These are some of the key points.

• Always go into competition fully fuelled with carbohydrate
• Well-fuelled athletes perform for longer at higher intensities than those with depleted reserves
• Basic biochemistry: fat burning is too slow and supplies of the phosphocreatine are too small to sustain intensities over 85% of VO2max
• Theory is backed up by experiment
• There are pros and cons to training with low levels of carbohydrate
• Positive effects: Improved fat burning, changes in cell signalling, gene expression and enzyme/protein activity, potential to save precious glycogen stores for crucial attacks later in a race
• Negative effects: Inconsistent evidence of improved performance, ability to complete training session may be compromised, reduced immunity, risks to bone health, loss of top end for those on high fat/low carb (ketogenic) diet
• Different ways to train with low carbohydrate
• doing two sessions in one day with minimal refuelling
• low carb evening meal and breakfast: sleep low, train low the next morning
• fasted rides
• high fat/low carb diet

Is there a structured method of training that provides the benefits without the negatives?

• The authors propose a glycogen threshold hypothesis
• Positive effects seem to be dependent on commencing with muscle glycogen levels within a specific range
• Levels have to be low enough to promote positive effects
• But when too low, protein synthesis may be impaired and the ability to complete sessions is compromised
• This leads to the idea of periodising carbohydrate consumption, meal by meal, around planned training sessions
• “Fuelling for the work required”
• low carbs before and during lighter training sessions
• high carbs in preparation for and during rides with greater intensities
• always refuel after training
• The diagram above provides an example for an elite endurance cyclist
• The red, amber, green colour coding indicates low, medium or high carbohydrate consumption
• On day 1, the athlete aims to “train high” for a hard session
• A lighter evening meal on day 1 prepares to “sleep low, train low” ahead of a lower intensity session on day 2
• Carbohydrate intake rises after exercise on day 2 in anticipation of a high intensity session on day 3
• Fuelling is moderated on the evening of day 3 as day 4 is assigned as a recovery day
• Carbohydrate rises later on day 4 to prepare for the next block of training
• The Pillar app aims to provide these leading edge scientific principles to amateur cyclists and other athletes

In order to put this into action, you need to know how much carbohydrate you are consuming. My assumption has been that my diet is reasonably healthy, but I have never actually measured it. So I have been experimenting with free app MyFitnessPal that can be downloaded onto your phone. This provides a simple and convenient way to track the nutritional composition of your diet, including a barcode scanner that recognises most foods. You can link it to other apps such as Training Peaks to take account of energy expended. However, neither of these tools plans nutrition ahead of training sessions. Pillar aims to fill this gap. It will be interesting to see whether this turns out to be successful.

## References

Fuel for the Work Required: A Theoretical Framework for Carbohydrate Periodization and the Glycogen Threshold Hypothesis, SG Impey, MA Hearris, KM Hammond, JD Bartlett, J Louis, G Close, JP Morton, Sports Med (2018) 48:1031–1048, https://doi.org/10.1007/s40279-018-0867-7

Fuel for the work required: a practical approach to amalgamating train-low paradigms for endurance athletes, Impey SG, Hammond KM, Shepherd SO, Sharples AP, Stewart C, Limb M, Smith K, Philp A, Jeromson S, Hamilton DL, Close GL, Morton JP, Physiol Rep. 2016 May;4(10). pii: e12803. doi: 10.14814/phy2.12803

Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers, Burke LM, Ross ML, Garvican-Lewis LA, Welvaert M, Heikura IA, Forbes SG, Mirtschin JG, Cato LE, Strobel N, Sharma AP, Hawley JA.  J Physiol. 2017;595:2785–807

Low energy availability assessed by a sport-specific questionnaire and clinical interview indicative of bone health, endocrine profile and cycling performance in competitive male cyclists, BMJ Open Sport & Exercise Medicine,https://doi.org/10.1136/bmjsem-2018-000424